WO2021087535A1

WO2021087535A1 - Method for manufacturing a porous film

Info

Publication number: WO2021087535A1
Application number: PCT/AT2019/060374
Authority: WO
Inventors: Markus Ungerank
Original assignee: Creonia E.U.
Priority date: 2019-11-05
Filing date: 2019-11-05
Publication date: 2021-05-14
Also published as: JP2023501342A; JP7473641B2; US20220393302A1; KR20220093356A; EP4055658A1; CN114631223A

Abstract

The present invention relates to a method for manufacturing a single-layer or multi-layer porous film, said method comprising the following steps: a) providing a flowable first base mixture for a first film layer of the film, the first base mixture comprising a solvent, a filler that is insoluble in the solvent, and a polymeric binder that is dissolved in the solvent; b) forming a film precursor film, the film precursor film comprising at least one sub-layer composed of the first base mixture; c) bringing the film precursor film into contact with a precipitant, the solvent of the first base mixture being soluble in the precipitant, the binder being insoluble in the precipitant, and the binder being precipitated to form the porous film. The invention also relates to a film manufactured using said method, an electrode material manufactured from said film, and an energy storage medium comprising said electrode material.

Description

Process for the production of a porous film

The present invention relates to a method for producing a porous film according to the independent patent claim. The invention further relates to a film produced using the method according to the invention, an electrode material which comprises this film, and an energy storage medium which comprises this electrode material.

Lithium (li) ion batteries are considered to be the key to the further expansion of the areas of electromobility and stationary power storage. The advantage of Li-ion technology is, among other things, the significantly higher energy and power density compared to other energy storage systems as well as low self-discharge.

The production of Li-ion batteries known in the prior art, however, is associated with considerable production engineering challenges, which arise, among other things, from extreme precision requirements, for example with regard to the layer thicknesses of the individual electrodes. In addition, known Li-ion batteries usually require complicated manufacturing steps. The variety of cell types available on the market increases the complexity even further. According to estimates, two-thirds of the costs are attributable to the material used in series production that is usual in the prior art. The way to lower production costs can therefore lead to higher throughput, fewer rejects and cheaper cathode materials.

A significant limiting aspect is the production of the individual components for the battery cells or batteries. In the prior art, the cathode, anode and the electrically insulating separator arranged between the cathode and anode are manufactured separately for the manufacture of lithium battery cells and then processed into cells of different geometries in a complex process.

The thickness of the anode and cathode is limited by the process, since the manufacturing process in the prior art involves the evaporation of a solvent, for example in a belt furnace. If the thickness of the foils produced in this way increases, uniform evaporation of the solvent is no longer guaranteed and the electrodes can have an inhomogeneous structure, which impairs their quality. Thicker coatings of anodes and / or cathodes also lead to increased equipment costs due to longer drying distances, since the evaporation time of the solvent increases quadratically with the thickness of the coating. Thicker electrodes or foils for electrode materials would, however, be desirable in order to improve the storage capacity of the Li-ion batteries.

It is an object of the present invention to solve this conflict of objectives and to create a method which enables the production of thicker foils with constant quality, the foils preferably being suitable for the production of electrode materials for Li-ion batteries.

This object is achieved by a method with the features of the independent patent claim.

The present invention thus relates to a method for producing a single-layer or multi-layer porous film.

If necessary, the following procedural steps are provided: Providing a flowable first base mixture for a first film layer of the film, the first base mixture comprising a solvent, an additive that is insoluble in the solvent and a polymeric binder dissolved in the solvent,

- Forming a foil precursor film, the foil precursor film comprising at least one partial layer from the first base mixture,

Bringing the foil precursor film into contact with a precipitant, the solvent of the first base mixture being soluble in the precipitant, the binder being at least partially insoluble in the precipitant, and the binder being precipitated so that the porous foil is formed.

If necessary, it is provided that the method additionally comprises the provision of a flowable first base mixture:

Providing a flowable second base mixture for forming a second film layer, the second base mixture comprising a solvent, an additive that is insoluble in the solvent, and a polymeric binder dissolved in the solvent, and

- providing a flowable third base mixture for forming a separating layer, the separator mixture comprising a solvent and a polymeric binder dissolved in the solvent,

It is optionally provided that the foil precursor film comprises a second partial layer from the second base mixture and a third partial layer from the third base mixture, the partial layers running parallel to one another in the main direction of extent of the foil precursor film.

It is optionally provided that the binder of the base mixtures is at least partially insoluble in the precipitant, the binder being precipitated so that the porous film is formed.

If necessary, it is provided that the third base mixture is essentially free of electrically conductive components or is electrically non-conductive. If necessary, it is provided that, in order to form the foil precursor film, the third base mixture is arranged between the first base mixture and the second base mixture.

It is optionally provided that the polymeric binder of the base mixture (s) comprises or consists of polysulfones, polyimides, polystyrene, carboxymethyl cellulose, polyether ketones, polyethers, polyelectrolytes, fluorinated polymers, in particular polyvinylidene fluoride, or a mixture of at least two thereof.

It is optionally provided that the solvent of the base mixture (s) comprises or consists of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, N-ethylpyrrolidone, sulfolane, dimethyl sulfoxide, methanol, ethanol, isopropanol, water or a mixture of at least two of them.

If necessary, it is provided that the aggregate is an electroactive agent.

It is optionally provided that the electroactive agent comprises or consists of a lithium oxide and / or a lithium sulfide and / or a lithium fluoride and / or a lithium phosphate, in particular lithium manganese dioxide, lithium cobalt dioxide, lithium nickel manganese cobalt dioxide, lithium nickel cobalt -Aluminium oxide, lithium nickel manganese spinel, lithium nickel manganese dioxide, lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate or any mixture thereof.

It is optionally provided that the electroactive agent comprises or consists of graphite, graphene, silicon nanoparticles, lithium titanate, tin or a mixture thereof.

It is optionally provided that the base suspension additionally comprises a conductivity agent, the conductivity agent comprising or consisting of conductive carbon, in particular carbon black, graphene or graphite. It is optionally provided that the precipitating agent comprises or is formed from water, at least one alcohol, for example methanol, ethanol, isopropanol, the solvent of a base mixture, or a mixture thereof.

It is optionally provided that the formation of the foil precursor film comprises the carrierless extrusion of the base mixture (s), preferably the carrierless co-extrusion of the first base mixture, the second base mixture and the third base mixture.

It is optionally provided that after step (b) and before step (c) the foil precursor film is brought into contact with a preprecipitation agent on one or both sides, in particular coated over the entire area, the binder of the base mixture (s) being insoluble in the preprecipitation agent.

It is optionally provided that the method additionally comprises the step: washing the film in a washing solution, the washing solution preferably comprising or being formed from water or at least one alcohol, for example methanol, ethanol, isopropanol or a mixture thereof.

If necessary, it is provided that the method additionally comprises the step: drying the film in a drying device, preferably a belt or roller dryer, with circulating air or an inert gas.

It is optionally provided that the method additionally comprises the step: compacting the film in a pressing device, a rolling device or a calendering device, preferably under the action of a temperature greater than 50 ° C. or compacting the film by thermal shrinkage.

The invention also relates to a porous film produced using a method according to the invention. It is optionally provided that the film has a preferably essentially constant thickness between 50 μm and 1000 μm, preferably between 200 μm and 500 μm.

It is optionally provided that the film comprises a first film layer, a second film layer and a separating layer arranged between the first and the second film layer, the first film layer and the second film layer having a thickness between 20 μm and 500 μm, and the separating layer being a Thickness between 5 gm and 50 gm.

If necessary, it is provided that the separating layer is an electrical insulator.

If necessary, it is provided that the first film layer and the second film layer is an electrical conductor.

The invention further relates to an electrode material comprising a film according to the invention, as well as a current-conducting layer arranged on the outer surfaces of the electrode material.

The electrode material optionally comprises at least two layers of a film according to the invention.

The invention also relates to an energy storage medium comprising an electrode material according to the invention, as well as an electrolyte and two contacting elements.

Further features of the invention emerge from the description, the patent claims, the exemplary embodiments, the figures and the preferred aspects of the invention.

In the method according to the invention, a first base mixture can be provided which is formulated to form a first film layer. The first base mix can comprise at least one solvent, an additive that is insoluble in the solvent, and a polymeric binder dissolved in the solvent.

It is advantageous if the film produced by the method according to the invention is a multilayer film. The step of assembling the individual electrodes to produce a cell is then not necessary and a possible source of error is eliminated. In addition, compared to the production of individual layers, the mechanical stability of the film is increased and individual partial layers can, if necessary, be made thinner.

Accordingly, in addition to the first basic mixture, a second basic mixture can also be provided. The second base mixture can comprise at least one solvent, an additive which is insoluble in the solvent, and a polymeric binder dissolved in the solvent.

In addition to the first basic mixture and the second basic mixture, a third basic mixture can also be provided. The third base mixture can comprise at least one solvent and a polymeric binder dissolved in the solvent. The third base mix can be free from insoluble additives. The third base mixture can alternatively comprise insoluble additives, which are preferably electrically non-conductive.

In addition to the first, second and third base mixes, other base mixes can also be provided, depending on the requirements for the final film product.

For example, a fourth and a fifth base mixture can be provided, which are designed to form discharge protection layers. The fourth and fifth base mixture can be arranged between the first and third or between the second and third partial layer when the foil precursor film is being formed. The fourth and fifth base mixture can in particular comprise a polymeric material with a low melting point as a binder. In particular, the melting point of this binder is below 100.degree. C., preferably below 80.degree. In a preferred embodiment it is provided that the first base mixture is designed to form an anode material, the second base mixture is designed to form a cathode material and the third base mixture is designed to form a separating layer arranged between cathode material and anode material. The anode material and the cathode material are preferably electrically conductive. The separating layer is preferably electrically insulating.

Accordingly, the first base mixture and the second base mixture preferably contain conductive components, in particular conductive additives that are insoluble in the solvent. The additives can particularly preferably be electroactive agents, can take up or release ions, preferably can take up or release lithium ions. The third base mixture preferably does not contain any conductive components. The third base mixture can, however, contain additives which are insoluble in the solvent, but which are preferably not electrically conductive. These additives or fillers can improve the stability of the separating layer in further processing steps. If necessary, however, the third base mixture cannot contain any insoluble additives.

The individual components of the basic mixtures can be the same, partly the same or completely different. For example, the first base mixture can comprise a polyimide as the polymeric binder and N-methylpyrrolidone as the solvent, while the second base mixture comprises polystyrene as the polymeric binder and dimethylformamide as the solvent.

Foil precursor films can be formed from the base mixtures. The base mixtures preferably have a viscosity which allows the base mixtures to be extruded, the base mixtures to be knife-coated or another method known in the prior art to be used for forming thin layers.

The base mixture (s) can, independently of one another, have a viscosity that is greater than 10 ² mPa ^* s, preferably greater than 10 ³ mPa ^* s, more preferably greater than 10 ⁴ mPa ^* s. The foil precursor film is preferably a multilayer foil precursor film which comprises several partial layers. The sub-layers run essentially parallel to one another and there is no significant mixing of the sub-layers. Depending on the solubilities, a certain mixing of the components of the individual sub-layers can take place in the areas near the interface.

The foil precursor film is preferably formed by coextruding the base mixtures.

After the foil precursor film has been formed, it is brought into contact with a precipitant, preferably immersed in it. The binder (s) of the base mixtures are at least partially insoluble in the precipitant, so that the binder (s) is / are precipitated on contact with the precipitant. This reverse phase reaction can cause the formation of a porous film. The physical properties of the film are largely dependent on the degree of insolubility of the binder or the binder in the precipitant.

As a result, a self-supporting film is formed, which preferably does not require any supporting medium. If the precursor film is produced by an extrusion process, the resulting porous film can be obtained as a continuous sheet material.

The film can preferably have a plurality of partial layers, in particular a first film layer, a second film layer and a separating layer arranged between the first and the second film layer. The composition of the first film layer is derived in particular from the first base mixture, the composition of the second film layer from the second base mixture and the composition of the separating layer from the third base mixture.

In a preferred embodiment of the film, the first film layer is an anode layer, the second film layer is a cathode layer and the third film layer is a separator layer. The cathode layer can in particular comprise a lithium metal oxide or a lithium metal phosphate as an electroactive agent. If discharge protection layers are provided between the cathode layer and the separating layer or between the anode layer and the separating layer, these can prevent the discharge of an energy storage medium at a certain temperature. If the cell temperature exceeds the melting point of the binder of the discharge protection layers, this penetrates into the pores of the separating layer and closes them so that no charge exchange can take place between the cathode layer and the anode layer.

Additional method steps can be provided in order to further improve the manufacturing method according to the invention.

Before it is brought into contact with the precipitating agent, the foil precursor film can be brought into contact with a pre-precipitating agent on one or both sides. This can have different solubility properties than the precipitant and thereby initiate a first precipitation step. Bringing into contact with the preprecipitating agent can take place directly before bringing into contact with the precipitating agent, for example by spraying the precursor film with the preprecipitating agent. If necessary, different preprecipitating agents can be applied to both sides of the precursor film. The preprecipitating agent can also be extruded in addition to the base mixes.

The preprecipitating agent can optionally have the same composition as the precipitating agent.

By applying the preprecipitation agent, rapid coagulation of the binder in the outer layers of the foil precursor film can be achieved. In this way, a skin-like surface can be formed which can suppress fluctuations in the thickness and a taper in the width of the film obtained upon extrusion. In addition, the use of a preprecipitation agent allows the porosity and the wettability of the surface of the film to be adjusted in a targeted manner. The final coagulation of the binder and the formation of the porous film take place in the precipitant, which is preferably contained in a precipitation bath. The pore structure of the film can be varied by setting parameters such as binder concentration in the base mixes, type of solvent used in the base mixes, composition of the precipitant, temperature of the precipitant, etc.

The porous film formed can optionally be transported further via an arrangement of rollers or cylinders. Optionally, after the film has been formed, the film can be introduced into a washing solution in order to remove precipitants, solvents and other impurities.

If necessary, the film can be passed through a further washing bath after washing in order to displace the detergent or the washing solution of the first washing bath. If necessary, the film can be passed through a dryer after the washing baths in order to evaporate the detergent or the washing solution.

The high porosity of the film and the low boiling point of the detergent facilitate and accelerate the evaporation of the detergent from the film.

If necessary, the film can be compacted in a pressing device, for example a rolling device or a calendering device, in order to compress the film. The compaction can also take place under the action of heat, for example at a temperature which is above the softening point of at least one binder, with or without a pressing device.

The film obtained by the method according to the invention can have a high porosity. The porosity of the first and second film layers can independently of one another be greater than 0.10, greater than 0.20, greater than 0.30, greater than 0.40, greater than 0.50, greater than 0.60, greater than 0 .70, greater than 0.80, or greater than 0.90.

The porosity of the first and the second film layer can independently of one another be less than 0.99, less than 0.95, or less than 0.90. In one embodiment, the porosity of an anode layer is between 0.2 and 0.4. In one embodiment, the porosity of a cathode foil is between 0.5 and 0.7.

The porosity of the separating layer can in particular be greater than the porosity of the first and second film layers. A high porosity of the separating layer leads to low resistances, which is advantageous in relation to a low cell resistance. The porosity of the separating layer can be greater than 0.20, greater than 0.30, greater than 0.40, greater than 0.50, greater than 0.60, greater than 0.70, greater than 0.80, or greater than Be 0.90. The porosity of the separating layer can be less than 0.99, less than 0.95, or less than 0.90. In one embodiment, the porosity of the separating layer is between 0.2 and 0.4.

The pores can be distributed homogeneously in the individual film layers, but a gradual pore size distribution and / or porosity distribution can also be provided, for example if a preprecipitation agent is used in the felling process. The parts of the film near the surface can then have a different porosity with pores of different sizes than the parts further inside. The above information on porosity relates in particular to the average porosity of the film layers.

The average pore size of the film layers and the separating layer can be, independently of one another, between 100 nm and 5 μm, in other exemplary embodiments between 500 nm and 2 μm, in other exemplary embodiments between 200 nm and 1 μm.

The film according to the invention can be further processed into an electrode material for an energy storage medium. For this purpose, a metallic current-conducting layer can be applied to the outer surfaces of the film, for example by lamination or by vapor deposition. The current dissipation layers can be formed from aluminum, copper, or other materials known for Li-ion batteries. If necessary, the multilayer films produced using the method according to the invention can be processed into a multilayer film composite in order to form a multilayer battery cell with increased cell voltage. The battery cell according to the invention can therefore optionally comprise two, three, four, five or more layers of a porous multilayer film according to the invention.

As a result, energy storage media with particularly high energy densities can be produced, with the amount of metals required for current dissipation being able to be further reduced. An electrode material that comprises such a multilayer film composite can in particular only be provided with current-conducting layers on its outermost layers. A metallic coating of the internal porous foils can be dispensed with if the surface of the foils is impermeable to lithium ions, which is the case, for example, when certain preprecipitating agents are used.

The multi-layer electrode material can then be built into an energy storage medium. In addition, two contacting elements are attached to the electrode material and the material is loaded with an electrolyte. The electrolyte fills the pores of the foil and enables the conduction of Li ⁺ ions.

In connection with the present invention, the term “dissolved” can mean that a component or a substance is completely solubilized in an agent, in particular in a solvent, that is to say that this component or this substance is not in solid form.

In connection with the present invention, the term “insoluble” can mean that a component or a substance is not soluble in a liquid. Optionally, negligible constituents, such as less than 0.5%, preferably less than 0.1%, more preferably less than 0.01%, can be soluble, so that a constituent or a substance is considered insoluble. In connection with the present invention, the term “electrically conductive” can mean that a material or substance has an electrical conductivity of more than 10 ⁴ S / m, preferably more than 10 ⁵ S / m, more preferably more than 10 ⁶ S / m.

In connection with the present invention, the terms “electrically insulating” or “electrically non-conductive” can mean that a material or substance has an electrical conductivity of less than 10 ⁶ S / m, preferably less than 10 ⁷ S / m, more preferably less than 10 ⁸ S / m.

In connection with the present invention, the terms “foil”, “film”, “membrane” and the like can be used synonymously.

Further optional aspects of the invention are given below. These aspects can be provided individually or in any combination in connection with the present invention.

According to a first optional aspect, the process is a continuous process.

According to a second optional aspect, the aggregate is suspended in the base mix or mixes.

According to a third optional aspect, the at least one conductivity agent is suspended in the base mixture or the base mixtures.

According to a fourth optional aspect, the aggregate and / or the conductivity agent are formed from nanoparticles or comprise nanoparticles.

According to the fourth aspect of the invention, the nanoparticles can be silicon nanoparticles which preferably have an average size of 10 nm to 200 nm, more preferably 50 nm to 100 nm. According to a fifth optional aspect, the base mixtures have different compositions.

According to a sixth optional aspect, at least one binder is a crosslinkable polymer. If appropriate, the crosslinkable polymer is swellable when it absorbs an electrolyte.

According to a seventh optional aspect, the binder is wholly or at least partially a polyelectrolyte with carboxylic and / or sulfonic acid groups.

According to an eighth optional aspect, the method for forming the film from the film precursor material is a phase inversion method for coagulating the binder.

According to a ninth optional aspect, the base mixture (s) are extruded with a slot die or with several slot dies or a multi-channel slot nozzle. The width of the nozzle (s) is preferably between 5 cm and 200 cm, particularly preferably between 10 cm and 50 cm.

According to one embodiment of the ninth optional aspect, a preprecipitation agent can be provided in further slot nozzles or in further channels of the multi-channel slot nozzle.

According to a tenth optional aspect, the temperature of the precipitant can be between 0 ° C and 80 ° C, in other aspects between 10 ° C and 50 ° C, in other aspects between 40 ° C and 80 ° C, in other aspects between 30 ° C and 60 ° C.

According to an eleventh optional aspect, the extrusion speed of the foil precursor film can be between 2 m / min and 50 m / min.

According to a twelfth optional aspect, the bringing into contact in step (b) of the method can comprise introducing or dipping the precursor film into the precipitant. According to a thirteenth optional aspect, a pretreatment of the base mixture (s) can be carried out before step (a) of the method.

According to the thirteenth aspect, the pretreatment may include one or more of the following:

- Deagglomeration of the base mixture (s), for example using a toothed disk stirrer and / or by means of ultrasound treatment,

- Filtration of the base mixture (s), for example using an edge filter, a candle filter, a fabric filter, or the like,

- Degassing of the basic mixture by means of vacuum, either directly or through a membrane.

According to a fourteenth optional aspect, the method can additionally comprise one or more of the following steps:

Washing step, optionally guiding the film material over pulleys or rollers, optionally guiding a washing solution in countercurrent to the movement of the film material

- drying step to evaporate detergents, solvents, preprecipitants, precipitants and other volatile components,

- Compression step to adjust the porosity of the foils by means of temperature treatment and / or pressing,

- Rolling up step to form a film roll, optionally with the arrangement of a spacer material between the individual film layers.

According to a fifteenth optional aspect, the third base material can comprise an electrically non-conductive or electrically inactive aggregate, for example silicon oxide and / or aluminum oxide.

According to a sixteenth optional aspect, the film according to the invention is a polymer composite material.

According to a seventeenth optional aspect, the film of the invention is a sheet material. According to an eighteenth optional aspect, the film according to the invention is a self-supporting film with a foam-like structure between the particles of the aggregate.

According to a nineteenth optional aspect, the electrode material comprises a current dissipation layer made of copper or aluminum, optionally with a thickness of less than 20 μm, preferably less than 5 μm, and particularly preferably less than 1 μm.

According to a twentieth optional aspect, at least one current dissipation layer is produced by metal vapor deposition, the vapor deposition process optionally being carried out continuously.

According to a twenty-first optional aspect, at least one current dissipation layer is produced by a galvanic metal coating.

According to a twenty-second optional aspect, the side surfaces of the energy storage medium according to the invention are sealed by melting the binding agent or by applying an adhesive.

According to a twenty-third optional aspect, the contacting elements are formed from a nickel strip and / or from aluminum strips that are connected to the electrode material with conductive adhesive or are welded to the electrode material.

The invention is explained in detail below on the basis of exemplary embodiments. In connection with the exemplary embodiments:

1 shows a schematic process flow diagram of a second exemplary embodiment of a method according to the invention;

2: a schematic representation of an energy storage medium which comprises a film produced by the method of the second exemplary embodiment. Unless otherwise indicated below, the following elements are shown in the figures: dissolving container 1, homogenizer 2, candle filter 3, storage container 4, line 5, extrusion device 6, line 7, precipitation liquid container 8, precipitation bath 9, circulating pump 10, deflection roller 11, washing bath 12, drying oven 13, winding device 14, electrode material 15, contacting element 16, cell housing 17, anode layer 18, cathode layer 19, separating layer 20, foil precursor film 21, foil 22, roll 23, metal layer 24, degassing device 25.

example 1

According to a first exemplary embodiment, a method for setting up a single-layer porous film is provided. Two of these foils are used to make an energy storage medium.

The compositions of the base mixtures of the two films are given in Table 1.

Table 1

The graphite has an average particle diameter of about 15 μm, the lithium iron phosphate of about 2.0 gm and the carbon black of about 0.05 μm.

Two basic mixtures are prepared, the powdery binder first being dry-mixed with the insoluble particulate solids, i.e. the electroactive agent and the conductivity agent. The powder mixture thus produced is then added to the solvent. The mixture is homogenized and then filtered through an ultrasonic sieve to remove any Separate agglomerates that have a size of more than about 50 gm. The suspension is degassed in vacuo.

Each base mixture is applied to a glass plate with a doctor blade in order to form a foil precursor film with a single partial layer. The thickness of the first partial layer produced in this way is about 250 gm for the anode foil and about 350 gm for the cathode foil.

The glass plate with the single-layer foil precursor film is then immersed in a bath with precipitant at room temperature, deionized water being used as the precipitant. After a residence time of about 10 minutes in the precipitant, the glass plate is removed from the precipitation bath. The foils with dimensions of about 30x20 cm can be removed manually from the glass plate. After a washing step in a washing bath with deionized water, the films are air-dried.

The films obtained are characterized by means of scanning electron microscopy. An average pore size of about 1.5 μm is determined. The porosity of the film produced is about 0.65. The thickness of the foils is about 145 gm for the anode foil and 150 gm for the cathode foil. Sample pieces of the single-layer anode and cathode foils with a size of 70 mm × 70 mm are pressed between two plane-parallel steel plates at room temperature in a Flebel press with a pressure of 0.3 to / cm ^2. The thickness of the anode foil after pressing is about 70 gm with a porosity of about 0.32, the thickness of the cathode foil is about 100 gm with a porosity of about 0.45. The films do not lose their good mechanical properties and flexibility.

The basis weight of the anode foil is around 100 g / m ² , the basis weight of the cathode foil is around 180 g / m ² , which is two to three times as much as the basis weight of anode or cathode coatings produced using the classic method an evaporation of the solvent in a belt dryer. An electrode material is formed from the foils by arranging a separating layer made of a commercially available polyethylene membrane (e.g. from Celgard) between an anode foil and a cathode foil. An aluminum foil is arranged as a current discharge layer on the surface of the cathode foil and a copper foil is arranged on the surface of the anode foil.

The electrode material is processed into a pouch cell as an energy storage medium in a form known in the prior art. The cells obtained have a typical cell voltage and several charge and discharge cycles are possible.

Example 2

According to a second exemplary embodiment, a further method for producing a single-layer porous film is provided. Two of these foils are used to make an energy storage medium.

The compositions of the base mixtures of the two films are given in Table 2.

Table 2

The graphite has an average particle diameter of about 1.5 gm, the lithium nickel cobalt manganese oxide of about 4.0 gm and the carbon black of about 0.05 μm.

Two basic mixtures are prepared, the powdery binder first being dry-mixed with the insoluble particulate solids, i.e. the electroactive agent and the conductivity agent. Then the so produced Powder mixture added to the solvent. The mixture is homogenized and then filtered through an ultrasonic sieve in order to separate any agglomerates it may contain, which have a size of more than approximately 50 μm. The suspension is degassed in vacuo.

Each base mixture is applied to a glass plate with a doctor blade in order to form a foil precursor film with a single partial layer. The thickness of the first partial layer produced in this way is about 140 gm for the anode foil and about 210 gm for the cathode foil.

The films obtained are characterized by means of scanning electron microscopy. An average pore size of about 1.5 μm is determined. The porosity of the films produced is about 0.55 for the cathode foil and 0.62 for the anode foil. The thicknesses of the foils are about 100 gm for the anode foil and 100 gm for the cathode foil. Sample pieces of the single-layer anode and cathode foils with a size of 70 mm × 70 mm are pressed between two plane-parallel steel plates at room temperature in a Flebel press with a pressure of 0.1 to / cm ^2. The thickness of the anode foil after pressing is about 85 gm with a porosity of about 0.56, the thickness of the cathode foil is about 85 gm with a porosity of about 0.47. The films do not lose their good mechanical properties and flexibility.

The weight per unit area of the anode foil is about 80 g / m ² , the weight per unit area of the cathode foil is about 139 g / m ² , which is about twice as high as the weight per unit area of anode or cathode coatings produced according to classic process with evaporation of the solvent in a belt dryer.

An electrode material is formed from the foils by arranging a separating layer made of a commercially available polyethylene membrane (e.g. from Celgard) between an anode foil and a cathode foil. An aluminum foil is arranged as a current discharge layer on the surface of the cathode foil and a copper foil is arranged on the surface of the anode foil.

Example 3

According to a second exemplary embodiment, a method for producing a multilayer porous film is provided. This film is used to make an energy storage medium.

In a step of the method according to the invention, a foil precursor film is produced which consists of three sub-layers, each sub-layer being formed from a base mixture. The compositions of the base mixtures are given in Table 3.

Table 3

The graphite has an average particle diameter of about 15 μm, the lithium iron phosphate of about 2 gm and the carbon black of about 0.05 μm.

The production method according to the invention in accordance with this second exemplary embodiment is illustrated in a process flow diagram in FIG. 1.

The base mixes are prepared by first completely dissolving the binder in the solvent. The binder solutions are produced in the dissolving containers 1a, 1b, 1c. In the case of the first and the second base mixture, the insoluble particulate solids, that is to say the electroactive agent and the conductivity agent, are then added and the mixture is homogenized in the homogenizers 2a, 2b. All three base mixtures are then filtered through candle filters 3a, 3b, 3c in order to separate off any agglomerates or other solids with a particle size of over 30 μm that may be present.

The base mixtures produced are then introduced into storage containers 4a, 4b, 4c, where they can be stored until further processing. Agitators are provided in each of the storage containers 4a, 4b, 4c in order to ensure the homogeneity of the base mixtures and to prevent particulate constituents from settling. The base mixtures are passed in separate lines 5a, 5b, 5c to an extrusion device 6, which is designed as a multi-slot extruder with five slot nozzles each 15 cm wide. In the lines 5a, 5b and 5c there are respectively degassing devices 25a, 25b, 25c, in this case degassing membranes.

The base mixes are introduced into the three central nozzles, the third base mix being arranged centrally between the first base mix and the second base mix.

The two outermost nozzles are connected to precipitation liquid containers 8a, 8b via lines 7a, 7b. In this exemplary embodiment, the precipitating liquid is deionized water and is brought into contact with the surfaces of the foil precursor film 21 emerging from the extrusion device 6 during the extrusion. This leads to a pre-precipitation of the binding agent even before contact with the actual precipitation bath 9.

The foil precursor film 21 is introduced free-standing into the precipitation bath 9, in which the precipitation liquid is contained. In this case the precipitating liquid is deionized water with about 2% of the solvent dimethylacetamide. The precipitation liquid is circulated in the precipitation bath by means of a circulating pump 10 and set in motion. Excess precipitation liquid leaves the precipitation bath 9 via an overflow and is pumped off and disposed of. The temperature of the precipitation bath is around 40 ° C.

The porous three-layer film 22 produced by the coagulation of the binding agent is passed out of the precipitation bath via a deflection roller 11 and transferred to a washing bath 12 via a further deflection roller 11. The film 22 is then dried in a drying oven 13 at about 80 ° C. and wound onto a roll 23 using a winding device 14. The web material obtained in this way can be fed to further use.

The films obtained are characterized by means of scanning electron microscopy. An average pore size of about 1.5 μm is determined. The porosity of the multilayer film produced is approximately 0.65 for the anode and cathode layers and approximately 0.85 for the separating layer in between. The total thickness of the film is about 350 μm. Sample pieces of the three-layer film with a size of 70 mm × 70 mm are pressed between two plane-parallel steel plates at room temperature in a lever press with a pressure of 0.3 to / cm ^2. The thickness of the film after pressing is approximately 180 μm, the anode layer being approximately 70 μm, the thickness of the cathode film approximately 100 μm and the separating layer approximately 10 μm thick. The foils do not lose their good mechanical properties and flexibility during compression.

The weight per unit area of the multilayer film is approximately 290 g / m ² .

The outer film layers, that is to say the cathode layer and the anode layer, have a porosity of approximately 0.45 and 0.32, respectively. The mean pore diameters are about 1.5 mih. The inner film layer, i.e. the separating layer, has a porosity of approximately 0.65. The mean pore diameter is about 2.5 gm.

To form an electrode material, pieces of the web material 15x10 cm in size are vapor-deposited on both sides with an approximately 1 gm thick metal layer. The surface of the anode layer receives a copper coating, while the surface of the cathode layer receives an aluminum coating.

The electrode materials produced in this way can be further processed into energy storage media. An exemplary energy storage medium is shown in FIG. 2. FIG. 2 is merely a sketched representation of an energy storage medium, the actual size relationships not being shown true to scale.

The electrode material 15 is contacted on the metal layer 24 of the anode and cathode side with contacting elements 16a, 16b, which are designed as nickel electrodes on the anode side, while aluminum contacting elements are used on the cathode side. This arrangement is packaged airtight in a cell housing 17. The electrode material 15, with the anode layer 18, the cathode layer 19 and the separation layer 20, is loaded with an electrolyte which ^{provides free Li +} ions as landing carriers. The wetting takes place through the capillary action of the pores in the film.

Compared to energy storage media produced according to the prior art, the production costs for the production of this energy storage medium according to the invention are approximately 20 to 25% lower. The mass-related storage density is over 50% higher than that of conventional energy storage media and the power-related space requirement is more than 20% lower.

The method according to the invention and the products obtained therefrom may result in the following additional advantages over the prior art: - The porosity of the layers is independent of the particle size of the aggregates used. It is therefore possible to use nanoparticles as additives in order to produce cells for high charge and discharge currents and to enable high diffusion speeds of the lithium ions in the pores.

- The precipitation process of the binder in the precipitating agent creates a sponge-like elastic structure between the aggregates, which gives the sub-layers strength and toughness. Cracks in the setting and in operation of the materials are greatly reduced.

The separating layer can be designed to be particularly thin and highly porous, since it is present as a partial layer and as such does not have to be mechanically loadable.

- The reduction of the metal content results in a weight reduction of the cell.

The reduced thickness of the separating layer and an increase in the porosity of the separating layer lead to a reduction in the ohmic internal cell resistance and thus to a lower power loss when charging and discharging the battery.

- The lower internal cell resistance allows faster charging compared to the prior art with less heating of the cell. At the same time, faster discharges (high power cells) can also be achieved.

- The process allows the use of materials with high softening points and temperature resistance such as. B. aromatic polyimides, polyamides, polyether ketones or polyether sulfones for the production of separators and electrodes. As a result, there is increased safety during operation due to the increase in the melt-down temperature.

Claims

1. Method of making a single-layer or multi-layer porous

A film comprising the following steps: a. Providing a flowable first base mixture for a first film layer of the film, the first base mixture comprising a solvent, an additive that is insoluble in the solvent and a polymeric binder dissolved in the solvent, b. Forming a foil precursor film, the foil precursor film comprising at least one partial layer from the first base mixture, c. Bringing the foil precursor film into contact with a precipitant, the solvent of the first base mixture being soluble in the precipitant, the binder being at least partially insoluble in the precipitant, and the binder being precipitated so that the porous foil is formed.

2. The method according to claim 1, characterized in that

- that the method additionally comprises for providing a flowable first base mixture: o providing a flowable second base mixture for forming a second film layer, wherein the second base mixture comprises a solvent, an additive that is insoluble in the solvent, and a polymeric binder dissolved in the solvent, and o providing a flowable third base mixture for forming a separating layer, the separator mixture comprising a solvent and a polymeric binder dissolved in the solvent,

that the foil precursor film comprises a second partial layer from the second base mixture and a third partial layer from the third base mixture, the partial layers running parallel to one another in the main direction of extent of the foil precursor film, and

- That the binder of the base mixtures is at least partially insoluble in the precipitant, the binder being precipitated so that the porous film is formed.

3. The method according to claim 2, characterized in that the third base mixture is essentially free of electrically conductive components or is electrically non-conductive.

4. The method according to claim 2 or 3, characterized in that to form the foil precursor film, the third base mixture is arranged between the first base mixture and the second base mixture.

5. The method according to any one of claims 1 to 4, characterized in that the polymeric binder of the base mixture (s) polysulfones, polyimides, polystyrene, carboxymethyl cellulose, polyether ketones, polyethers, polyelectrolytes, fluorinated polymers, in particular polyvinylidene fluoride, or a mixture of at least two of them includes or consists of.

6. The method according to any one of claims 1 to 5, characterized in that the solvent of the base mixture (s) dimethylacetamide, dimethylformamide, N-methylpyrrolidone, N-ethylpyrrolidone, sulfolane, dimethyl sulfoxide, methanol, Etahnol, isopropanol, water or a mixture of at least includes or consists of two of them.

7. The method according to any one of claims 1 to 6, characterized in that the aggregate is an electroactive agent.

8. The method according to claim 7, characterized in that

- that the electroactive agent comprises or consists of a lithium oxide and / or a lithium sulfide and / or a lithium fluoride and / or a lithium phosphate, in particular lithium-manganese dioxide, lithium-cobalt dioxide, lithium-nickel-manganese-cobalt dioxide, lithium-nickel-cobalt-aluminum oxide, Lithium-nickel-manganese spinel, lithium-nickel-manganese dioxide, lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate or any mixture thereof, and / or that the electroactive agent comprises or consists of graphite, graphene, silicon nanoparticles, lithium titanate, tin or a mixture thereof.

9. The method according to any one of claims 1 to 8, characterized in that the base suspension additionally comprises a conductivity agent, wherein the conductivity agent comprises or consists of conductive carbon, in particular carbon black, graphene or graphite.

10. The method according to any one of claims 1 to 9, characterized in that the precipitating agent comprises or is formed from water, at least one alcohol, for example methanol, ethanol, iso-propanol, the solvent of a base mixture, or a mixture thereof.

11. The method according to any one of claims 1 to 10, characterized in that the formation of the foil precursor film comprises the carrierless extrusion of the base mixture (s), preferably the carrierless co-extrusion of the first base mixture, the second base mixture and the third base mixture.

12. The method according to any one of claims 1 to 11, characterized in that the foil precursor film after step (b) and before step (c) is brought into contact with a preprecipitation agent on one or both sides, in particular coated over a large area, the binder being the Base mixture (s) is insoluble in the preprecipitant.

13. The method according to any one of claims 1 to 12, characterized in that the method additionally comprises the following step: d. Washing the film in a washing solution, the washing solution preferably comprising or being formed from water or at least one alcohol, for example methanol, ethanol, isopropanol or a mixture thereof.

14. The method according to any one of claims 1 to 13, characterized in that the method additionally comprises the following step: e. Drying the film in a drying device, preferably a belt or roller dryer, with circulating air or an inert gas.

15. The method according to any one of claims 1 to 14, characterized in that the method additionally comprises the following step: f. Compacting the film in a pressing device, a rolling device or a calendering device, preferably under the action of a temperature greater than 50 ° C or compacting the film by thermal shrinking.

16. Porous film produced by a method according to any one of claims 1 to 15.

17. The film according to claim 16, characterized in that the film has a preferably essentially constant thickness between 50 μm and 1000 μm, preferably between 200 μm and 500 μm.

18. The film according to claim 16 or 17, characterized in that the film comprises a first film layer, a second film layer and a separating layer arranged between the first and the second film layer, the first film layer and the second film layer having a thickness between 20 μm and 500 μm pm, and wherein the separating layer has a thickness between 5 pm and 50 pm.

19. Film according to one of claims 16 to 18, characterized in that the separating layer is an electrical insulator.

20. Film according to one of claims 16 to 19, characterized in that the first film layer and the second film layer is an electrical conductor.

21. Electrode material comprising a film according to one of claims 16 to 20, as well as a current dissipation layer arranged on the outer surfaces of the electrode material.

22. Electrode material according to claim 21, comprising at least two layers of a film according to one of claims 16 to 20.

23. Energy storage medium comprising an electrode material according to claim 22, as well as an electrolyte and two contacting elements.